Flash lamp



March 31, 194

C. W. PATTON FLASH LAMP Filed Aug. 3, 1940 -COMBUS T/BLE MA TERI/4L GLASS ENVELOPE HAVING AN INNER COA TING CONTAINING LOW wscosl 7') POL rw/vn 405m TE INVENTOR CARL W. PATTON BY v ATTORNEY u mm 5R m- M m GL ASS ENVELOPE INNER COA TING CON TA/N/NG LOW VISCOSITY POLYV/NVL ACETATE Patented Mar. 31, 1942 barren stares, PATENT orrics rmsn LAMP Carl W.'Patton, Palisades Park, N. 3., assignor to Carbide and Carbon Chemicals Corporation, a corporation of New York Application August 3, 1940, Serial No. 351,184

8 Claims. (CI. 67-31) gen. The combustion process may be initiated by the passage of an electric current through a tungsten wire to which is cemented a mixture of zirconium oxide and lead peroxide, the cementing material usually being cellulose nitrate or some other inflammable organic substance. The tungsten ignition wire must be in contact with the foil or wires of combustible material at all times in order to insure against delayed firing or complete failure in firing. The glass bulb or envelope is sealed into a conventional screw or bayonet type base to which the lead wires are attached, and through which the bulb may be connected to a source of electrical current.

Flash bulbs are fabricated from thin-walled glass and the disposition of the combustible material within the bulb is such that unequal heating may occur, the resulting stress occasionally being so great that the bulbs explode and endanger the operator. A further disadvantage of the present construction is that the combustible material may change its position with relation to the ignitionwire in the course of normal handling of the bulb before it is put into use and this displacement is sometimes enough to cause delayed firing or total failure to fire.

It has hitherto been the practice to minimize the danger of flash bulb explosions by coating the flash bulbs with cellulose nitrate on cellulose acetate or mixtures of these substances. These materials adhere to the broken particles of glass and prevent their broadcast dispersion. One of the disadvantages encountered with the use of these cellulose derivatives is their instability to light and heat. Cellulose nitrate and acetate films darken very rapidly when the combustible material is fired and the passage of light is impeded and varied with a consequent lowering of the quality of photographs taken.

. The objects of my invention are to reduce the danger of bulb explosion and delayed firing and at the same time to insulate the combustion material from the walls of the bulb.

In the accompanying drawing, Fig. l is a side vention can be attained and a superior type of flash bulb provided by coating the inside surface of the glass wall with a composition of polymerized vinyl acetate or with compositions containing a mixture of polymerized vinyl acetate with cellulose nitrate. Flash bulbs treated with my composition have practically no tendency to shatter or splinter-if the glass bulb explodes and at the same time the danger of explosion from unequal heating is greatly reduced because of the heat insulating action of the resinous coating which operates to equalize heating stresses. The

resinous coating accomplishes further important 7 by adhering to the combustible material and holding it firmly in place.

The compositions I have discovered aremuch more stable to light and heat than the cellulose derivative films hitherto employed. As a result there is substantially no impedance or variation of light supply and photographs taken are of a higher quality than has hitherto been possible.

My compositions consist of relatively concentrated solutions of resinous materials which can be applied to the bulbs by spraying or dipping and from which the coating forms-on evaporation of the solvent liquid. I have found that low viscosity polyvinyl acetate resins are the most satisfactory materials.

The different grades of polyvinyl acetate refer to the degree of polymerization of the monomer, vinyl acetate. A convenient index of the degree of polymerization is furnished by the viscosity in centipoises at 20 C. of a standard molal (based on the molecular weight of the monomeric vinyl acetate) solution of the resin in benzene. For example, a solution (or dispersion) of 86 grams (the gram molecular Weight of the monomer) of polyvinyl acetate of grade 25 in sufiicient benzene to make one liter of-solution will have a viscosity of 25 centipoises at 20 C. .By a low viscosity polyvinyl acetate I mean a polymerized vinyl acetate resin having a viscosity not greater than about '7 centipoises at 20 C. as determined by the method set forth.

It is possible to employ the polyvinyl acetate resins alone or in mixture with cellulose nitrate in the proportions of from five to two parts of polyvinyl acetate to one part of cellulose nitrate; Coatings made from such mixtures are substantially non-inflammable and have increased strength and hardness. I prefer to use those cellulose nitrates of relatively low nitrogen content for the reason that these have proved to be somewhat more stable to heat and light than forms of cellulose nitrate of a higher nitrogen content.

In certain cases it may be desirable to increase the flexibility or softness of the coatings and this can be accomplished economically and expeditiously by incorporating small amounts of plasticizers with the resin solutions. I have found thatsubstances of the class represented by di(ethoxyethoxyethyl) phthalate, dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, and di(bu toxyethyl) phthalate are useful for this purpose.

The following examples serve to illustrate the invention. In each case the coating was formed on the interior of the flash bulb by a single spray application or by dipping the bulbs in the compositions described before the combustible material in the form of wire or foil was placed in the bulb. On heating the bulbs to seal them in their bases the resinous coating became tacky enough to adhere to the combustible material at the points where the foil or wire came into contact with the coating. When the bulb were cooled the coating hardened, firmly cementing the combustible material to the walls of the bulb.

Example 1 A by weight solution of polyvinyl acetate in acetone yielded a good coating. Acetone can be replaced by any of the volatile solvents for polyvinyl acetate such as isopropyl acetate. ethyl acetate, ethyl alcohol, butyl alcohol, butyl acetate, benzene or toluene or appropriate mixtures of the foregoing.

Example 2 A solution of the following composition gave an exceptionally good coating:

Per cent Low viscosity polyvinyl acetate (grade 2.5) 21.2 Cellulose nitrate of a nitrogen content of 10.8-11.1%, and a viscosity of 5 seconds as measured by the Standard A. S. T. M.

specification D301-33'I' for testing nitrocellulose 5.32 Alcohol to wet the cellulose nitrate in storage 2.28 Di(ethoxyethoxyethyl) phthalate 2.65 Isopropyl acetate 24.3 Denatured ethyl alcohol 44.25

By weight 100.00

This composition was diluted with 33 parts of a mixture of equal parts of isopropyl acetate and ethyl acetate per 100 parts'of compostion and was applied with an ordinary compressed air spray gun.

As many apparently widely different embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that I do not limit myself to the foregoing examples or descriptions, except as indicated in the following claims.

I claim:

1. A flash lampcomprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising low viscosity polyvinyl acetate, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

2. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of low viscosity polyvinyl acetate resin and cellulose nitrate resin, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

3. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of a low viscosity polyvinyl acetate resin and a plasticizing material, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

4. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of a low viscosity polyvinyl acetate resin, cellulose nitrate and a plasticizing material, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

5. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of a low viscosity polyvinyl acetate resin and at least one of the materials of the group consisting of di(ethoxyethoxyethyl) phthalate, dioctyl phthalate, dibutyl phthalate and di(butoxyethyl) phthalate, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

6. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of a low viscosity polyvinyl acetate resin and tricresyl phosphate, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

7. A flash lamp comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of a low viscosity polyvinyl acetate resin, cellulose nitrate, and at least one of the materials of the group consisting of di(ethoxyethoxyethyl) phthalate, dioctyl phthalate, dibutyl phthalate and di(butoxyethyl) phthalate, 'said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired.

8. A fiash bulb comprising a glass bulb containing a combustible material and combustion supporting means, said bulb being coated on its inner surface with a film comprising a mixture of a low viscosity polyvinyl acetate resin, cellulose nitrate and tricresyl phosphate, said film being transparent, capable of securing the combustible material in place, and adapted to reduce the dangers of shattering when the bulb is fired CARL W. PATTON. 

